1. Field of the Invention
This invention relates to an endoscope image data compressing apparatus for compressing endoscope image data,
2. Description of the Related Art
Endoscopes have recently come to be extensively used in medical and industrial fields.
In the medical field, generally, endoscope images are recorded so that an endoscope image in the case of an inspection with an endoscope may be later investigated in detail. In such a case, the endoscope image is photographed but electric recording and reproducing apparatuses, such as a VTR and photodisc apparatus easy to record/reproduce images, are extensively used.
Generally, image information requires a recording capacity far greater than in the case of recording character information and therefore there are problems that, if an image is recorded so as to be able to be reproduced with a high fidelity, the number of recordable image sheets will become small and that, in the case of transmitting an image, the transmitting speed will be low.
Therefore, in the publication of Japanese Patent Application Laid Open No. 1700/1990 there is suggested an image compressing and expanding apparatus wherein, at the time of recording, image data will be compressed and recorded but, at the time of reproducing, the compressed data will be expanded and will be displayed on a television monitor.
An example of an endoscope system including the above-mentioned image compressing and expanding apparatus shall be explained in the following with reference to FIGS. 97 to 99.
FIG. 97 is a schematic view of an entire endoscope system comprising an electronic endoscope apparatus and image recording apparatus. An endoscope 891 inserted in a living body 892 is connected to an observing apparatus 893 to which are connected an observing monitor 894 and an image recording apparatus 896, including an image data compressing apparatus. A sucker 895 is connected to the endoscope 891.
FIG. 98 shows a flow of an image signal in the endoscope 891 and observing apparatus 893. The image signal from a CCD 901 in the tip part of the endoscope 891 enters an amplifier 902, is amplified to a voltage level in a predetermined range, then enters a .gamma. circuit 903 and has the .gamma. corrected. In the case of an RGB frame sequential system, the signal having had the .gamma. corrected is analog-digital converted by an A/D converter 904, then enters a selector 905 and has R, G and B recorded in respective memories 906R, 906G and 906B. The image signals having had R, G and B recorded in the respective memories 906R, 906G and 906B are called out by the timing of a TV signal and are respectively digital-analog converted by D/A converters 907R, 907G and 907B. The image signals of R, G and B, having been converted to analog signals, are transmitted to RGB output terminals R, G and B together with a synchronizing signal (SYNC) of a synchronizing signal generating circuit 913. The thus obtained RGB signals are displayed in a monitor 894 to make an endoscope observation. Also, these RGB signals can be recorded by an image recording apparatus 896.
When a white color light of a lamp 910 is passed through a rotary filter 909 rotated by a motor 911, respective red, green and blue color passing filters provided in this rotary filter 909 will be interposed in the light path and lights of respective wavelengths of red, green and blue will be radiated to a light guide 903 of said endoscope 891. Therefore, image signals imaged under respective illuminating lights of red, green and blue will be written into R, G and B memories 906R, 906G and 906B. The motor 911, A/D converter 904, selector 905, memories 906R, 906G and 906B, D/A converters 907R, 907G and 907B and synchronizing signal generating circuit 913 are all controlled by a control signal generating part 912.
FIG. 99 shows a flow of an image signal in an image recording apparatus 896. The image signals from the RGB signal output terminals R, G and B are input into an input part of the image recording apparatus 897. The RGB signals are analog-digital converted by an A/D converter part 898 through a switching switch and are then led to a compressing circuit 899 utilizing a compression theory, such as predictive coding. The compressed image data are recorded in such recording system part 920 as a photodisc or photomagnetic disc. In the case of reproducing the images, the image data on the recording system part 920 are restored to the original image signals in an expanding circuit part 921. The image signals are then digital-analog converted by a D/A converter part 922 and are transmitted to an output part 923. On the other hand, a control signal generating part 924 controls the destinations of the image signals and the transferring timing at the time of transferring the image signals and is connected to the A/D converter part 898, compressing circuit part 899, recording system part 920, expanding circuit part 921 and D/A converter part 922. Also, from the control signal generating part 204, a synchronizing signal (SYNC) is transmitted to the input part 897 and output part 923.
Now, an imaging device, such as an imaging means of an electronic endoscope, has various numbers of pixels and therefore the spatial frequency of the obtained image may be different depending, for example, on the kind of the unit of the electronic endoscope. Also, the size and shape of the endoscope image on a television monitor may be different depending on the kind of the unit of the electronic endoscope.
In a conventional image compressing apparatus, there are problems in that the data obtained from an endoscope, for example, having a large number of pixels will be compressed in excess but, on the contrary, the data obtained from an endoscope of a small number of pixels will be too small in the compressing rate to make an efficient compression.
In the picture on the monitor, there is often another portion of the screen which is not part of the effective image corresponding to an endoscope image. If a compression is made by excluding such portion, a high compression will be possible but, because the size and shape of the endoscope image on the television monitor are different depending on the kind of the unit of the electronic endoscope, various endoscope images cannot be treated with one compressing mode.
Also, the endoscope image varies in the characteristics with the observing position and method. However, in the conventional image compressing apparatus, the compression is in only one mode and therefore an optimum compression will not always be made and the picture quality deteriorates depending on the image.
Now, today there are suggested various compressing means. Among them, there is a predictive coding means whereby, in the compression of an endoscope image having no movement at all or very small movement, if any, on the picture, the image is digitized, the value of pixels to be coded is predicted from the nearby pixels and the predictive error is quantized by use of a discrete cosine converting means. For example, in the compression of an endoscope image by the predictive coding means, the predictive error by the predictive coding of respective RGB is quantized as it is in an ordinary density gradation, for example, a density gradation of 5 bits. Now, in investigating an endoscope image, it is found that there are bright portions such as an adjacent body wall and dark portions such as a comparatively far body wall in or around a hole. In this endoscope image, the portion to be recorded in detail and to be required for the later observation and investigation is a bright portion. In a somewhat darker portion, noises are so many that the anticipation error need not be small or the minute part cannot be definitely observed and therefore, even if the compressing rate is elevated, there will be no trouble. When such an endoscope image is uniformly compressed, if the compressing rate is high, the picture quality of the bright part will deteriorate and, if the compressing rate is low, the data amount of the dark portion will also become large and the efficiency will be low.
Now, in an ordinary endoscope image, the image color is so reddish and the correlation between the adjacent pixels is so high that, when an ordinary compressing method is used, a high compression will be possible. However, an observing method wherein a part to be inspected is painted with such dyeing agent as methylene blue so that the affected part may be definitely observed has recently come to be used for the observation with an endoscope. When this observing method is used, in the observed image, a bluish color and reddish color will be present as mixed and the correlation between the adjacent pixels will be low. Therefore, there are problems that, if such an image is compressed the same as in the ordinary observed image, the picture quality will deteriorate and the compressing rate will be reduced.
Also, there has recently come to be used an observing method wherein such fluorescent agent as fluorescein is injected into a part to be inspected to observe a fluorescence emitted by this fluorescent agent. If this observing method is carried out in a frame sequential system in which an illuminating light is sequentially switched to R, G and B, a fluorescence will be emitted from the fluorescent agent at the time of the illumination of B and therefore the observed image will be an image in which a blue color will be present as mixed in an image based on a reddish color and which will be different from an ordinary observed image. Therefore, there are the same problems as at the time of observing the above-described dyed image.
Now, there are compressing methods, for example, wherein an intra-image correlation with an adjacent pixel within the same field or frame is utilized and wherein an inter-image correlation with an image of a past field or frame is utilized. In case the correlation between the present image and former image is large as in the case of recording a moving image, if the inter-image correlation is utilized, the image will be able to be efficiently compressed. On the other hand, in case the correlation between the present image and former image is small as in the case of recording an image in sometime after the former image is recorded, if said inter-image correlation is utilized, no image will be able to be efficiently compressed.
On the other hand, in case the correlation with the former recorded image is small, it will be effective to use the intra- image correlation but, in case the correlation with the former recorded image is large, the image will not be able to be compressed more efficiently than in the case of utilizing the inter-image correlation.